# The force exerted by a spring

If you try to stretch a spring, it will pull back against you. The farther you stretch the spring, the harder it pulls back. Can you make this simple description more quantitative?

1. Acquire one small silver spring. Measure its mass and its length as it lies horizontally at rest on the table.
2. Arrange clamps and bars as shown in the diagram above so that you can hang the spring from a horizontal bar. Measure the length of the spring as it hangs by itself; call this Lvert.
3. Place 7 various weights, ranging from 0 to 150 grams, on the bottom of the spring. Measure the length of the spring for each case. Compute the distance the spring has stretched from Lvert. Include uncertainties in this "distance stretched".
4. Calculate the force exerted by the spring in each case. Make a neat table of all your measurements and calculations.
5. Make a graph which shows force exerted by the spring as a function of the distance by which the spring has been stretched.

6. Use your graph to compute the "spring constant" or "force constant" of your spring. Include uncertainties, and make sure the units of your values make sense.
7. Walk around and talk to at least 3 other groups. Write down their spring constants (with uncertainties) and compare them to yours. Are all the springs in class today "identical"?

#### Prediction

At the center table, I will set up a track tilted at 15 degrees. We will attach your spring to the track so that it lies along the track, and then attach to the lower end a cart of mass m (I'll provide the actual mass during the class period).

How long will your spring be when it comes to rest, supporting the car on this tilted track? Make a prediction.

```

within                  this part will be
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+/- 2 cm                    +3

+/- 4 cm                    +2

+/- 6 cm                    +1
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```